Kort nozzle

ABSTRACT

A Kort nozzle, in particular a Kort nozzle configured rotatable around the rudder axis of a ship, wherein at least one opening is provided in the wall of the Kort nozzle, so that the occurence of recirculations or of swirls is avoided or reduced even with an angular position with respect to a longitudinal axis of the ship and a globally uniform flow pattern is adjusted as far as possible.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a Kort nozzle, in particular a Kortnozzle which is configured rotatable about the rudder axis of a ship.

2. Description of the Related Art

A Kort nozzle is a conically tapered tube in which the propeller of aship is placed. The tube also forms the wall of the Kort nozzle. Due tothe taper of the tube to the stern of the ship, the Kort nozzles cantransmit an additional thrust to the ship without the output having tobe increased. Besides the propulsion improving properties of the Kortnozzle, pitching by rough sea is thus reduced so that by sea disturbancethe loss of velocity can be reduced and the directional stability can beincreased. Since the inherent resistance of the Kort nozzle increasesapproximatively quadratically as the speed of the ship increases, itsadvantages are effective in particular for slow ships which have a bigpropeller thrust (for example tugboats, fishing vehicles, etc.).

Besides fixed Kort nozzles behind which normally a rudder is placed inflow direction for the control of the ship, there are so-called “Kortrudder nozzles” for which the Kort nozzle is rotatable about the rudderaxis of the ship which is in vertical direction. For this purpose,bearings are normally provided on the upper and lower side of the Kortnozzle on the outside of its wall for the rotatable positioning. Incontrast, the propeller is still fixed so that the Kort nozzle alsorotates around the propeller. Frequently, the Kort nozzle is connectedwith the rudder post and positioned in the rudder heel. It is normallyswivellable about a vertical axis of rotation or about the rudder axisby approximately 30° to 35° to both sides. Thus, the Kort nozzle is acombination of propulsion improving means and rudder since a ruddereffect is achieved by the excursion of the propeller jet at an angle tothe ship longitudinal axis. For excursed rudder nozzles, the stern ofthe ship is pushed by the jet reaction propulsion.

FIG. 5 illustrates an embodiment of a Kort nozzle 200 positionedrotatable about the rudder axis of a ship with a fixed propeller placedtherein as it is known from the prior art. The Kort nozzle 200 is placedaround the fixed ship propeller 210 of a ship (not represented here).Here the Kort nozzle is pivoted under an angle a of approximately 30°about the ship longitudinal axis 220. The arrow 221 represents the flowdirection of the sea water or salt water. A fixed flap 230 is providedin flow direction behind the propeller on the Kort nozzle 200, throughwhich the flow properties of the Kort rudder nozzle are positivelyinfluenced. Due to a reduced wall thickness, the inlet area 201 (withrespect to the direction of the flow passing through the Kort nozzle200) is configured widened with respect to the remaining area of theKort nozzle 200. This means that the inner diameter of the inlet area isbigger than the inner diameter in the remaining area of the Kort nozzle200. The water flow through the Kort nozzle 200 is increased which inturn increases the propulsion efficiency of the Kort nozzle.

Comprehensive calculations, tests and simulations of the applicantresulted in that, for certain twisting angles of a conventional Kortnozzle, swirls or recirculations of the flow form in the area directlybehind the propeller. These recirculations or swirls have adisadvantageous effect on the power of the Kort nozzle. They develop inparticular directly behind the propeller in the side area of thepropeller to which the Kort nozzle is turned. Due to the recirculationsthe flow rate of the water flowing through is considerably reduced inthis area so that the driving power of the Kort nozzle is reduced. Sincethe recirculations occur only in a locally limited side area and theflow runs substantially laminarly in the other areas as usual,considerable vibrations which can be transmitted to the hull of the shipand which have also a disadvantageous effect adjust. Reference is madehereunder to the FIGS. 6 a and 6 b for illustrating this problem.

FIG. 6 a shows schematically the topview of a cut Kort nozzle 200 as itis known from the state of the art. The arrows in FIGS. 6 a and 6 bconstitute the course of the flow. The ship propeller 210 is drawn onlyschematically for reasons of clarity. For this Kort nozzle 200, contraryto the Kort nozzle of FIG. 5, a movable or swivellable flap 231 isplaced in flow direction behind the propeller 210. The Kort nozzle 200is swivelled with an angle of approximately 15° with respect to the shiplongitudinal axis. The rear part of the wall 202 a of the Kort nozzle200 has been rotated against the flow direction, i.e. to the propeller210, while the opposed part of the wall 202 b has been rotated with theflow direction accordingly.

The lower part area of the Kort nozzle 200 which is marked in FIG. 6 ais depicted enlarged in FIG. 6 b. It can be recognized therein that, dueto the angular position of the Kort nozzle 200 with respect to thepropeller 210 or to the ship longitudinal axis 220, a swirl orrecirculation of the flow forms in the outer edge area in flow directiondirectly behind the propeller 210. Due to this recirculation, the meanflow rate in the main flow direction 221 is reduced to a minimum in thislocal area. Measurements and simulations in this area showed that thereis a mean flow rate of 0.2 to 2 m/s in the main flow direction 221.Compared to this, the mean flow rate is situated within a range of 12 to16 m/s in the area between the flap 231 and the wall area 202 b.

The water which flows laminarly outside along the wall 202 a flowsaround the rounded-off edge of the wall of the Kort nozzle end area 203to the inside and hits there the flow produced by the propeller 210which is directed in the main flow direction 221. A part of the outerflow is directed to the inside against the main flow direction 221 andflows on the inner side of the wall 202 against the main flow direction221 to the area behind the propeller 210 and from there back againthrough the propeller 210. Thus, a local circulation or recirculation ofthe flow is formed and the mean flow rate in the main flow direction 221in this area is around zero. Therefore, the disadvantages describedabove occur.

SUMMARY OF THE INVENTION

Starting from the prior state described above, the object of thisinvention is to provide a Kort nozzle for which the occurence ofrecirculations or swirls is avoided or reduced even with an angularposition with respect to the ship longitudinal axis and which has auniform over-all flow pattern.

In accordance with the present invention, at least one opening isprovided in the wall of the Kort nozzle.

In this context, with openings, basically any opening of anyconfiguration in the wall of the Kort nozzle is to be considered. Theopening extends through the whole wall and thus consists of an inner andof an outer opening area and a central area connecting these two areas.It is decisive that a flow connection is created for the sea water orthe salt water from outside the Kort nozzle through the at least oneopening into the inside of the Kort nozzle.

The wall of the Kort nozzle is formed by the nozzle ring which envelopsthe stationary ship propeller. Basically the at least one opening can beprovided at any location of the wall of the Kort nozzle. However,preferably it is provided in a lateral area of the Kort nozzle, eitheron the starboard side, or on the port side. It is decisive that the atleast one opening is configured provided or placed in the wall in such amanner that, due to the at least one opening, sea water or salt watercan flow from outside the Kort nozzle throughout this opening into theinside of the Kort nozzle in such a manner that the recirculations orswirls which develop at certain swivelling angles of the Kort nozzle aresuppressed or considerably reduced. Tests of the applicant resulted inthat, due to such openings, the thrust of the Kort nozzle has beenincreased in the side areas in which typically swirls or recirculationsoccur by up to 20%. Furthermore, the vibrations transmitted to the hullhave been reduced.

Due to the at least one opening, a laminar flow is thus introduced fromoutside to the critical side areas of the Kort nozzle in which theswirls typically occur at certain swivelling angles. This laminar flowavoids that a recirculation flow can be formed in the side areas againstthe main flow direction. The thrust and the working stability and thusthe efficiency of the Kort nozzle are considerably improved herewith.

In order to be able to suppress the occurence of swirls in anyswivelling direction, it is appropriate to provide at least two openingsin the wall of the Kort nozzle. Advantageously, both openings are placedsubstantially opposite each other. Appropriately, both openings aremoreover to be placed respectively in a side area of the Kort nozzlesince normally the strongest swirls develop there for conventional Kortnozzles. It is thus guaranteed that the risk of the occurence of swirlsor recirculations is reduced for a swivelling to the starboard side aswell as for a swivelling to the port side.

With respect to the height of the Kort nozzle, according to a preferredembodiment of the invention, the at least one opening is disposed in acentral area. This being, the central area ranges from one third of theheight of the Kort nozzle to approximately two thirds of the Kortnozzle, preferably from two fifths to three fifths of the height of theKort nozzle. It is thus achieved that the at least one opening is placedin an area in which the swirls typically occur. Thus, the laminar flowflowing through the at least one opening can develop an optimal effectand can suppress the swirl as much as possible. According to theinvention, it is particularly preferred to provide a central arrangementof the at least one opening with respect to the height of the Kortnozzle. This being, the height of the Kort nozzle corresponds to itsvertical extension when mounted, i.e. to the distance between theopposed wall areas of the Kort nozzle along its vertical axis or alongthe rudder axis.

The central areas of the Kort nozzle extend in their longitudinalextension over the whole length of the Kort nozzle. There are thus twocentral areas which are placed opposite to each other. According toanother preferred embodiment of the invention, at least two openings aredisposed in at least one of these two central areas. Furthermore, theseat least two openings are placed in longitudinal direction of the Kortnozzle the one behind the other and/or in vertical direction lying aboveone another. Depending on the configuration of the Kort nozzle and ofthe propeller as well as the respective swivelling angle, the result tobe achieved can thus be optimized, namely the improvement of the thrustand of the quiet running of the Kort nozzle. For this embodiment too, atleast two openings are respectively provided in both central areas,whereby the openings of both central areas are advantageously placedopposite to each other.

With respect to the length of the Kort nozzle, i.e. the dimensions ofthe Kort nozzle, when the Kort nozzle is not swivelled about the shiplongitudinal axis, according to another preferred embodiment, the atleast one opening is disposed in an area from one third to two thirds ofthe length, preferably from two fifths to three fifths of the length,particularly preferably in the middle. The effect of the at least oneopening can again be optimized by this measure too.

For a swivellable Kort nozzle with a fixed ship propeller placedtherein, it is furthermore preferred to configure the at least oneopening in such a manner that it is placed, for a swivelling angle of10°, 15° or 20°, with its inner opening area substantially adjacent tothe propeller. It is thus guaranteed that, for the above mentionedtypical swivelling angles, the laminar flow which comes out of the inneropening area of the at least one opening, flowing from the outside tothe inside into the Kort nozzle, hits directly the swirl area. Thelaminar flow can thus directly act against the recirculation flow andthe effect of the at least one opening is further improved. Should insome cases other swivelling angles, for example 25° or 30°, be employed,the arrangement of the at least one opening can naturally be adaptedaccordingly.

For the further optimization of the effect of the at least one openingfor the efficiency of the Kort nozzle, it is provided in a furtherpreferred embodiment of the invention to configure the at least oneopening as an oblong slit. Moreover, it is advantageous that theslitlike opening substantially extends in the vertical direction. It isthus achieved that a vertically orientated flow band flows into the Kortnozzle from the outside to the inside and thus positively influences thecritical area in which normally swirls develop. Furthermore, such anopening can be produced relatively easily.

Furthermore, it is preferred that the at least one opening extendsobliquely from the outside to the inside with respect to the main flowdirection through the wall. This means that the middle line of theopenings is orientated with a predetermined angle to the main flowdirection or to the longitudinal axis of the Kort nozzle. It is thusguaranteed that the outer laminar flow flows from the outside to theinside into the Kort nozzle and that no water flows from the inside tothe outside through the at least one opening.

It is preferred in particular to configure the at least one opening withrespect to the longitudinal axis of the Kort nozzle with an angle of 10°to 60°, preferably 20° to 45°, particularly preferably 30° to 35°. Theindications of angles refer to the angle between the longitudinal axisof the Kort nozzle and the middle line of the at least one opening whichextends from the outside to the inside through the at least one opening.

For a further preferred embodiment of the invention, it is provided thatthe at least one opening tapers from the outer side of the wall or fromits outer opening area to its inner opening area on the inner side ofthe wall. The speed of the flow which flows from outside into the Kortnozzle can thus be increased so that the overall efficiency of the Kortnozzle and the risk of the occurence of turbulences or recirculationsare further reduced.

Alternatively, the at least one opening can be configured substantiallyconstant over its whole extension.

Appropriately, at least one of the admission edges and/or at least oneof the discharge edges of the at least one opening is to be configuredrounded-off. In the flow direction, each opening has, for example for aslitlike vertically orientated opening, two vertically orientatedadmission edges and two vertically orientated discharge edges. Theadmission through the opening into the Kort nozzle is thus improved inso far as the risk that unwished swirls can occur on the admission ordischarge edges due to a breakaway of the flow is reduced.

The various features of novelty which characterize the invention arepointed out with particularity in the claims annexed to and forming apart of the disclosure. For a better understanding of the invention, itsoperating advantages, specific objects attained by its use, referenceshould be had to the drawing and descriptive matter in which there areillustrated and described preferred embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWING

In the drawing:

FIG. 1 a is a schematic perspective view of a Kort nozzle with twoopposite openings which are positioned swivellable on the hull of aship;

FIG. 1 b is a schematic sectional view of a portion of the Kort nozzleof FIG. 1 a;

FIG. 2 a is a schematic perspective view of a Kort nozzle swivellablypositioned on a hull of a ship for which two openings situated insuccession in a horizontal direction are placed in each central area;

FIG. 2 b is a schematic sectional view of the Kort nozzle of FIG. 2 a;

FIG. 3 is a schematic perspective view of a Kort nozzle swivellablypositioned on the hull of a ship with respectively three openingssituated in succession in a vertical direction in each central area;

FIG. 4 is a schematic sectional top view of a portion of a Kort nozzlewith an opening with flow lines.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 a is a perspective view of a Kort nozzle 100 which is positionedswivellable on the hull 10 of a ship. The hull 10 of a ship is depictedonly partially for reasons of clarity. The Kort nozzle is connected withthe hull 10 by a bearing 12 and is rotatable about the rudder axis 11.The rudder axis 11 corresponds to the vertical axis. The Kort nozzle 100is furthermore connected with the hull in its lower area by a furtherbearing (not represented here). Considering the flow direction 13, amovable or controllable flap 14 follows at the end of the Kort nozzle100. The Kort nozzle 100 comprises a ring-shaped configured wall 15which is configured conically and which tapers in the flow direction 13.An opening 16 is placed respectively in the central side areas 15 a, 15b of the wall 15 with respect to the height of the Kort nozzle. Theopenings 15 are placed substantially in the middle with respect to theheight. The openings 16 extend obliquely from the outside to the inside,this being considered in the flow direction 13. They consist in a slitextending substantially vertically which tapers from the outside to theinside. Thus, the openings 16 have an approximately shovel-typeappearance since the outer opening area 16 a is wider than the inneropening area 16 b because of the taper of the opening 16. The propelleris omitted in FIG. 1 a for reasons of clarity but is placed, whenmounted, inside the Kort nozzle 100.

FIG. 1 b shows a sectional view of a portion of the Kort nozzle 100 ofFIG. 1 a. In particular, the wall of the Kort nozzle 100 of FIG. 1 b iscut in the area of an opening 16. It can be recognized that the opening16 extends in flow direction obliquely from the outside to the insideand that it tapers to the inside. Correspondingly, the outer openingarea 16 a is wider than the inner opening area 16 b. Among the twohorizontally extending admission edges 17 a, 17 b of the opening 16, therear admission edge 17 a is configured rounded-off while the frontadmission edge 17 b is configured angular. In the same way, the reardischarge edge 18 a is rounded-off in flow direction 13 while the frontdischarge edge 18 b is angular. When considered from the side, the outeropening area 16 a and the inner opening area 16 b of the opening areoffset to each other, in particular they are placed offset laterally toeach other. Thus, the inner opening area 16 b is covered by theobliquely extending side walls of the opening 16 or by the wall 15, withrespect to a side view of the Kort nozzle 100. In other words, theopening is configured as a slitlike channel which extends obliquely fromthe outside to the inside in flow direction 13.

FIG. 2 a shows a perspective view of a further embodiment of a Kortnozzle according to the invention 100. It can be recognized in FIG. 2 athat the flap 14 is supported in the upper rudder bearing 12 as well asin a lower flap bearing on the Kort nozzle 100. Furthermore, twoopenings 16 are respectively placed in the central areas 15 a, 15 b ofthe wall 15, openings which are situated one behind the other in a shiplongitudinal direction, when the Kort nozzle is not deviated, or in thelongitudinal direction of the Kort nozzle. It can be recognized in FIG.2 a that only the outer opening area of the openings 16 can be seen fromthe outside and the inner opening area is covered. Correspondingly, theouter and the inner opening area of the opening 16 are placed one behindthe other in flow direction 13.

FIG. 2 b shows a sectional view of the Kort nozzle 100 of FIG. 2 a. Itcan be recognized that the openings 16 are placed respectively oppositeeach other in both central areas 15 a, 15 b of the wall 15. Moreover,these openings 16 extend obliquely from the outside to the inside inflow direction 13. The single openings 16 are moulded respectivelyidentical and thus extend parallel to each other.

FIG. 3 shows a further embodiment of a Kort nozzle 100 according to theinvention. For this embodiment, three openings 16 placed one above theother in a vertical direction are provided in each central area 15 a, 15b of the wall 15. The openings 16 are placed respectively in the middlewith respect to the longitudinal direction of the Kort nozzle 100. Thedistance between the single openings 16 of a central area 15 a, 15 b isrespectively approximately the same.

FIG. 4 shows a flow pattern of a side area of a Kort nozzle 100 with aportion of a schematically depicted propeller 20. Overall, the depictionof FIG. 4 is similar to that of FIG. 6 b, whereby contrary to thedepiction of FIG. 6 b a Kort nozzle according to the invention with anopening 16 has been used. The represented arrows symbolize the flowcourse of the water flowing through the Kort nozzle. As it can berecognized, water flows from the outside to the inside through theopening 16. As soon as it passes the inner opening area 16 b of theopening 16 it flows further along the inner side of the wall 15 until itfinally leaves the Kort nozzle 100. Thus, no back circulation or swirlcan form in the area between the outside of the propeller 20 and the endside of the Kort nozzle 100 with respect to the flow direction 13. Onthe contrary, the whole flow flows laminarly inside the Kort nozzle 100and also outside on the edge of the Kort nozzle 100.

While specific embodiments of the invention have been shown anddescribed in detail to illustrate the inventive principles, it will beunderstood that the invention may be embodied otherwise withoutdeparting from such principle

1. In a Kort nozzle configured to be swivelable about a rudder axis of aship, wherein the Kort nozzle comprises a ring duct consisting of onesolid wall, said duct being conically tapered, and a bearing forswiveling the Kort nozzle about the rudder axis of a ship, wherein thewall of the duct has at least two openings which are disposedsubstantially opposite each other, wherein a a fixed ship's propeller isdisposed in the Kort nozzle so that the Kort nozzle is also swivelableabout the propeller, and wherein the at least two openings are bothalways unsealed and configured so that water flows simultaneouslythrough said at least two openings from outside to the inside of theKort nozzle.
 2. (canceled)
 3. The Kort nozzle according to claim 1,wherein the at least two openings are disposed in a central area withrespect to a height of the Kort nozzle.
 4. The Kort nozzle according toclaim 3, wherein the central area ranges from one third to two thirds ofthe height of the Kort nozzle.
 5. The Kort nozzle according to claim 4,wherein the central area ranges from two fifths to three fifths of theheight of the Kort nozzle.
 6. The Kort nozzle according to claim 3,wherein at least two openings are disposed in each central area of theKort nozzle, wherein the at least two openings of each central area arearranged in a longitudinal direction of the Kort nozzle one behind theother and/or in a vertical direction above one another.
 7. The Kortnozzle according to claim 1, wherein the at least two openings are eachdisposed with respect to a length of the Kort nozzle in an area from onethird to two thirds of the length.
 8. The Kort nozzle according to claim1, wherein the at least two openings are each disposed with respect to alength of the Kort nozzle in an area from two fifths to three fifths ofthe length.
 9. The Kort nozzle according to claim 1, wherein the atleast two openings are each disposed with respect to a length of theKort nozzle in an area in the middle of the length.
 10. (canceled) 11.The Kort nozzle according to claim 1, wherein for a swiveling angle of10°, 15° or 20° one of the at least two openings is disposedsubstantially adjacent to the propeller.
 12. The Kort nozzle accordingto claim 1, wherein the at least two openings are configured as anoblong slit extending in vertical direction.
 13. The Kort nozzleaccording to claim 1, wherein the at least two openings extend obliquelyfrom the outside to the inside through the wall with respect to a mainflow direction.
 14. The Kort nozzle according to claim 13, wherein theat least two openings extend at an angle of 10° to 60°, with respect tothe longitudinal axis of the Kort nozzle.
 15. The Kort nozzle accordingto claim 14, wherein the at least two openings extend at an angle of 20°to 45°, with respect to the longitudinal axis of the Kort nozzle. 16.The Kort nozzle according to claim 14, wherein the at least two openingsextend at an angle of 30° to 35°, with respect to the longitudinal axisof the Kort nozzle.
 17. The Kort nozzle according to claim 1, whereinthe at least two openings taper from the outer side of the wall to theinner side of the wall.
 18. The Kort nozzle according to claim 1,wherein the dimensions of the at least two openings are substantiallyconstant over the whole extension thereof.
 19. The Kort nozzle accordingto claim 1, wherein admission edges and/or discharge edges of the atleast two openings are rounded-off.
 20. Ship having a Kort nozzleaccording to claim 1.